A028682 Pseudo Galois numbers for d=20.

1, 380, 60648000, 3880986816000000, 99352641531709440000000000, 1017370731356251764129792000000000000000, 4167150450523480419075515127693312000000000000000000000, 6827459292803717741943269048796063017352560640000000000000000000000000000

Offset: 0

Author

Olivier Gérard

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..27

Crossrefs

Cf. A028668, A028670, A028671, A028672, A028674, A028676, A028677, A028678, A028680, A028683, A028684, A028686.

Programs

Mathematica

FoldList[ #1*20^#2 (20^#2-1)&, 1, Range[ 20 ] ]
a[n_] := 20^n * Product[20^n - 20^k, {k, 0, n-1}]; Array[a, 8, 0] (* Amiram Eldar, Jul 14 2025 *)

PARI

a(n) = 20^n * prod(k = 0, n-1, 20^n - 20^k); \\ Amiram Eldar, Jul 14 2025

Formula

a(n) = 20^n * Product_{k=0..n-1} (20^n - 20^k).

a(n) ~ c * 20^(n^2+n), where c = Product_{k>=1} (1 - 1/20^k) = 0.947500313281... . - Amiram Eldar, Jul 14 2025